This application relates to the use of displacement sensors in detecting mechanical motion.
In many signal acquisition systems, such as optical signal and RF signal acquisition systems, signal stabilization is critical for error-free data recovery. Signal stabilization is difficult to achieve when atmospheric or mechanical jitter exists in the acquisition system. Jitter can result both from movement of the signal source and movement of the signal reception system. For example, movement by a human operator is a common source of mechanical jitter in a video recording system, such as a handheld camcorder.
Signal reception systems used in interplanetary communication receive signals from distant sources at very high data rates. Those signals are often in the form of plane waves. The rates at which these systems can recover data accurately is limited by signal distortions that result from mechanical deformation and vibration of the reception systems. For earth-bound reception systems, common causes of mechanical deformation and vibration include gravitational weight redistribution during tracking and pointing, deflection caused by wind, thermal effects and gradients arising from solar heating and cooling, and stray mechanical resonance. The antennas in the U.S. deep space network, for example, include 34-meter and 70-meter mirrors that vibrate characteristically at a frequency of approximately 5-10 Hz with a deformation amplitude of approximately 1-2 cm.
Recognition of the above led the inventor to develop a signal acquisition system capable of detecting displacement in three dimensions and correcting received signals to compensate for this displacement. The system is useful in a wide variety of applications, including interplanetary communication with very large antenna systems that are subject to a wide variety of sources of mechanical deformation and vibration. In these systems, incoming signals can be corrected to compensate for distortions introduced by deformation and. vibration of the antennas. This in turn improves data transmission and recovery, in part, by reducing link noise temperatures and increasing bit transmission rates.
In one aspect, the invention involves measuring physical displacement in three dimensions with a displacement sensor. An optical signal source produces an optical signal, such as a pulse-modulated or frequency-modulated laser beam, having a characteristic feature that varies with linear distance traveled by the optical signal. The displacement sensor is positioned to receive at least a portion of the optical signal. The sensor produces an output signal indicating a position at which the optical signal strikes the sensor in each of two orthogonal dimensions. The sensor itself is subject to displacement in a third orthogonal dimension, such as the displacement caused by deformation of an antenna on which the sensor is mounted.
Processing circuitry is coupled to the sensor to derive information about the characteristic feature of the optical signal at the target sensor. The processing circuitry applies this information in calculating a linear distance traveled by the optical signal in the third orthogonal dimension and then derives from the linear distance an amount by which the target sensor has been displaced in the third orthogonal dimension.
Other embodiments and advantages will become apparent from the following description and from the claims.